The invention is directed to roller conveyor systems using gravity to move articles from an upper level to a lower level. More particularly, the present invention relates to a gravity powered spiral conveyor including means for assisting and controlling the movement of articles through the conveyor.
A conveyor in accordance of the invention provides an apparatus for automatically transporting articles from one level to a lower level or for accumulating articles in the conveyor based on article movement conditions. The conveyor of the invention can be used as part of a larger conveyor system and is readily adaptable for providing a range of height changes and direction changes. While the invention is preferably directed to a spiral conveyor, the inventive principles may be applied to other conveyor configurations, as will be appreciated by those skilled in the art, and the invention is not necessarily limited to the embodiments described below.
A conveyor in accordance with the invention includes a frame preferably defining a spiral conveying path from an upper level to a lower level. A conveying surface is provided by a plurality of freely rotatable rollers or skate wheels. A plurality of controllable, reversible powered rollers are individually disposed in the frame at predetermined intervals along the conveying path. Sensing means is mounted in the frame to detect the presence of conveyed articles adjacent each of the powered rollers. The powered rollers are controllable for assisting the gravity transport of the articles or for reversed rotation for accumulating articles in the conveyor when the downstream portion of the conveyor is full. Accumulate mode prevents articles from overloading the lower end of the conveyor when transport from the conveyor is blocked by holding the articles in the conveyor. This facilitates resumption of transport when the blocked condition is resolved.
According to the invention, a spiral conveyor includes a plurality of curved segments fastened to form a spiral path, each having a predetermined cant. The curvature and the cant of the segments can be selected so that the spiral executes a desired number of turns for a selected height change.
In accordance with a preferred embodiment of the invention, each of the segments is shaped to define a 90xc2x0 arc which simplifies manufacturing and assembly. The 90xc2x0 segment arcs provide a convenient size for the transport and accumulate modes of operation. In addition, 90xc2x0 arcs allow the entry segment and exit segment to be oriented at a convenient parallel or perpendicular direction to accommodate the directions of the feed and takeaway conveyors.
According to another aspect of the invention, a powered roller is included in each of the segments to control the movement of a conveyed article through the segment. The powered rollers are controllable to rotate alternatively in a forward direction to assist the transport of articles down the conveyor or a reverse direction to accumulate articles in the conveyor.
According to yet another aspect of the invention, sensing means is included to sense the presence of an article in each of the segments. A signal from the sensing means is used to control the powered rollers. Preferably, the sensing means comprises a plurality of sensors mounted in the conveyor with one sensor in each segment. The sensing means can be any suitable device, for example, a photocell or a mechanical switch.
A control means receives the signals from the sensing means and uses the signal to determine whether to activate the powered rollers for transport mode or accumulate mode depending on a comparison of the presence of articles in adjacent segments, that is, whether a downstream segment is clear to receive an article from the segment immediately upstream.
The control means operates in transport mode to activate a roller to rotate in a forward direction in a segment when the sensing means senses the presence of the article in the segment and senses that the downstream adjacent segment is clear.
In transport mode, the rollers rotate at a set speed in a direction for forward movement of the articles. Thus, articles of light weight that may have difficulty overcoming inertial or frictional forces on the conveyor are accelerated, and heavier articles that may move too fast for the takeaway conveyor to handle smoothly are slowed down by friction produced in moving across the powered roller.
The control means operates in an accumulate mode upon sensing that an article has remained in a segment for a predetermined length of time. When accumulate mode is activated, the control means activates the rollers in that segment to rotate in reverse to hold the article in the segment, and as an article is sensed in the immediately upstream segment, that roller is rotated in reverse. The control means continues to activate the segments in reverse sequence as long as a downstream blockage exists. When the downstream segment clears, the control means reverts to transport mode and activates the segments to resume moving articles forward in the same order in which they were set in accumulate mode.